1. Field of the Invention
The present invention relates to a novel acoustic insulator used in locations where acoustic considerations are needed and locations where prevention of entry and leakage of sound is desirable, and in more detail relates to an acoustic insulator utilizing a plastic coated with a magnetic material such as a magnetic tape or magnetic sheet, particularly waste material of the same.
2. Description of the Related Art
Conventionally, as acoustic insulators, there are fibrous sound absorbing materials such as glass wool and rock wool and aluminum and other metal and ceramic porous sound absorbing materials. Also, concrete materials have an acoustic insulation performance. Further, also sheet materials such as plywood, gypsum plaster board, particle board, and metal sheets are used as acoustic insulators. Also, for the purpose of improving the sound absorption property of specific frequencies, perforated sheets etc. have been used.
However, the fibrous sound absorbing materials such as the aforesaid glass wool and rock wool have a moisture absorption property and water absorption property. As the amount of absorbed moisture and amount of absorbed water increase, the sound absorption performance is reduced. Also, sound absorbing materials of metals, ceramics, and concrete are heavy and expensive, and therefore are naturally restricted in their conditions of use. Also, sheet materials and perforated sheets generally have a low sound absorption performance. Further, perforated sheets have been used for special purposes and cannot be used as general purpose acoustic insulators in practice.
On the other hand, the amount of use of plastic coated with a magnetic material such as magnetic tape and magnetic sheet has been increasing year by year. The disposal of that type of refuse has in particular become a problem. Moreover, in the process of production of plastic coated with a magnetic material, the increase in the amount of production is accompanied with an increase in the amount of the substandard products which are disposed of as waste. The method of disposal of that waste is also becoming a problem.
As the method of utilizing the waste of plastic coated with a magnetic material, the methods of Japanese Unexamined Patent Publication No. 63-199739, Japanese Unexamined Patent Publication No. 63-199740, etc. are known. However, the techniques disclosed in these publications are techniques of producing recycled plastic products using the waste plastic coated with the magnetic materials, for example, sheets for pavement of roads and vibration dampening sheets. The objects thereof are to obtain recycled plastic products. The obtained products could not be used as acoustic insulators having satisfactory sound absorption performance.